1. Field of the Invention
The present invention relates to an image recording apparatus for printing a visible watermark superimposed over an original image on recording medium.
2. Description of the Related Art
Recently, various types of multi-functional printers suitable for use at home, workplaces, etc. have been put on the market. Among these, printers intended to be used mainly at business offices are often provided with special functions such as xe2x80x9cwatermarkxe2x80x9d printing. A watermark is a faint design made in recording medium together with other substantial images printed on the recording medium. By employing this function, a phrase such as xe2x80x9cTop Secretxe2x80x9d or xe2x80x9cDraftxe2x80x9d may be printed on recording paper together with the original images (i.e., text, pictures, etc). FIG. 8 of the accompanying drawings shows an example of watermark (consisting of two Chinese characters meaning xe2x80x9ctop secretxe2x80x9d) superimposed over the original images, such as xe2x80x9c3. MARKET SCALExe2x80x9d, xe2x80x9c4. PROSPECTxe2x80x9d, and the accompanying text.
Conventionally, two different pieces of print data may be combined by using a function called xe2x80x9cOverlayxe2x80x9d or xe2x80x9cForm Overlay.xe2x80x9d By this function, as shown in FIG. 9 or 10, overlay data representing a table of a prescribed format may be superimposed over the original data to be filled in the table.
Specifically, the first technique shown in FIG. 9 makes use of a single full-page bitmap memory. In this method, the command-formed overly data supplied from a host computer is stored in a overlay data memory, while the documental (original) data is stored in a documental data memory. Then, the documental data is unfolded (converted) into bit-mapped data to be stored in the bitmap memory. Thereafter, the command-formed overlay data is converted into bit-mapped data and then superimposed over the bit-mapped documental data in the bitmap memory.
The other technique shown in FIG. 10 utilizes two full-page bitmap memories for storing the overlay data and the documental data, respectively. These two kinds of bit-mapped data are added by an OR circuit before being supplied to the print engine.
Each of the techniques described above is applicable to printing a watermark over an original image. For this, the formatted table data is simply replaced with the desired watermark data. However, this may give rise to the following disadvantages.
Specifically, according to the method shown in FIG. 9, the logical sum calculation for superimposing the watermark data over the original image data in the bitmap memory is performed with respect to all of the pixels for the entire page. Further, this logical sum calculation is performed as the command-formed water mark data is being unfolded into the bit-mapped data. Disadvantageously, such designing tends to make the printing speed unduly slow.
The method shown in FIG. 10, on the other hand, requires at least two full-page bitmap memories, which may lead to an unfavorable cost increase. Further, the watermark to be printed is typically much smaller than the print surface of the recording medium. This means that the watermark print data is present only in a small part of the watermark bitmap memory. This is a waste of the capacity of the watermark memory.
The present invention has been proposed under the circumstances described above, and its object is to provide an image recording apparatus capable of performing high-speed watermark printing without unduly increasing the capacity of required memory.
According to the present invention, there is provided an image recording apparatus for printing a visible watermark superimposed over an original image on recording medium. The recording apparatus includes: a first memory for storing watermark print information including positional data of the watermark; a second memory for storing watermark effective data; a third memory for storing original image data; an original image data reader for reading out the original image data from the third memory; and a watermark data reader for reading out the watermark effective data based on the watermark print information, wherein the read-out watermark effective data is superimposed over the read-out original image data.
With such an arrangement, the second memory does not need to have a large capacity since only the effective data of the watermark is stored therein.
According to a preferred embodiment, the watermark print information may include watermark print start raster line data watermark print start position data for raster lines, watermark print length data for the respective raster lines, and watermark print end flag. The watermark print length data may correspond to the watermark effective data. More specifically, the watermark print length data may represent the length of the watermark effective data.
Preferably, the image recording apparatus of the present invention may further comprise a watermark storage controller for causing the watermark print information to be stored in the first memory and for causing the watermark effective data to be stored in the second memory.
Preferably, the watermark print information may be obtained by preparing bit-mapped data of the watermark.
Preferably, the image recording apparatus of the present invention may further comprise original image data unfolding means for generating bit-mapped data of the original image in the third memory.
Preferably, the image recording apparatus of the present invention may further comprise an additional memory for storing the original image data read out from the third memory.
Preferably, the image reading apparatus of the present invention may further comprise an OR circuit for calculating logical sum of the watermark effective data and the original image data. With the use of such an OR circuit, the watermark effective data may not need to be superimposed on the original image data in a memory. Thus, no additional memory is needed, and high-speed superimposing performance with the watermark data and the original image data is achieved.
Preferably, the image reading apparatus of the present invention may further comprise a semiconductor memory chip, wherein at least two of the first, the second and the third memories are provided by mutually different storage regions of the semiconductor memory chip.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.